In valve devices known from practice, which are made with a valve housing having a plurality of recesses and a valve slide arranged to move longitudinally in the valve housing, depending on the geometry of the valve housing and the valve slide a pressure field is formed around the valve slide which is not symmetrical. Among other things the pressure field depends on the geometric shape of the valve slide, for example whether it is conical, straight or designed cylindrically. Furthermore, the pressure field also depends on bevels formed in the area of the valve housing bore. An unsymmetrical pressure field is formed, in particular, when recesses of the valve housing are produced by a casting process since in that case they are not rotationally symmetrical to the required extent. In the area of the valve slide unsymmetrical pressure fields result in radial and axial forces that act upon the valve slide and impair the functionality of the valve device.
To homogenize the pressure fields produced around the circumferential area of the valve slide, in the seal area between the valve slide and the valve housing, so-termed relief grooves are made in the surface of the valve slide, which are recesses that extend in the circumferential direction of the valve slide and are at least approximately groove-like. Although a pressure field is unsymmetrical as before as far as such a relief groove or furrow, in the area of the relief groove itself, the pressure field is constant. The pressure field is re-formed outside the relief groove. For that reason, in the circumferential direction around the slide, the more relief grooves provided in the area of the valve slide, the pressure field is more homogeneous. In turn, a homogeneous pressure field produces a rotationally symmetric force around the slide, which corresponds to a central force. The slide is then in an almost force-balanced operating condition and with low friction forces in the valve housing, it can be moved to the desired extend by small control forces.
Usually, by means of switching valves of hydraulic or pneumatic pressure systems, in each case a working pressure area can be connected alternately to a low-pressure area or a tank, or to a high-pressure area carrying a system pressure. For example a working pressure area is connected by way of a throttle device to a low-pressure area when the pressure in the working pressure area has to be vented toward the low-pressure area with defined pressure gradients. In such pressure systems, leaks between the high-pressure area carrying the system pressure and the working pressure area are disadvantageous when the working area is connected by means of the valve slide to the low-pressure area and the pressure in the working pressure area has to be reduced to the pressure level of the tank, since the leakage and thus also the venting time of a volume-affected consumption depend markedly on temperature and on the system pressure.
In general leaking always takes place in the area of a valve device when for example the gap size between the valve housing and the valve slide is large or the viscosity of the medium carried in the area of the valve device is very low. In such cases the leakage occurring in the area of the valve device is proportional to the pressure difference, to the third power of the gap size between the valve housing and the valve slide, and to the diameter of the valve slide. Furthermore, the leakage is inversely proportional to the viscosity of the medium and to the overlap length in the area between the valve slide and the valve housing.
To vent a working pressure area by way of a throttle device toward a low-pressure area with a defined gradient is necessary, for example, when a hydraulic end-position sensor of a bidirectionally actuated working piston is positioned upstream from the throttle device, since the quality of the sensor signal is influenced by the leaking in the area of the valve device. Such an end-position sensor system is known, for example, from the previously unpublished patent application DE 10 2010 028 762.8 by the present applicant.